This application claims foreign priority benefits of German priority document DE 100 48 962.1, filed on Oct. 4, 2000, and entitled xe2x80x9cPortable testing device for testing test-pieces operated at high voltages and/or currentsxe2x80x9d (translated and amended) to Hensler et al., the disclosure of which is incorporated by reference in its entirety.
The present invention relates to a portable testing device for testing test-pieces operated at high voltages and/or high currents, such for example as high-voltage or high-current transformers, over-current relays or the like.
Previous transportable testers that are able to supply high currents and voltages almost always constitute individual solutions for specific applications. High-current sources, for example, are known for measuring the transformation ratio of current transformers and for testing over-current relays. Also known are voltage sources for testing voltage transformers and for plotting current transformer magnetization curves, and xcexcxcexa9 measuring bridges or mxcexa9 measuring bridges.
Transportable testers giving output currents of up to a few amps and output voltages of up to a few kilovolts at an output power of up to a few kilovolt-amperes are currently all still constructed using conventional 50 Hz techniques. In this case, the testing signal, i.e. the testing current or testing voltage, is set manually or by a motor using a variable transformer. The testing signals supplied by the given tester depend on the waveform of the mains voltage, and where the test-pieces are non-linear, on the voltage-dependent impedance of the test-piece as well. This is an important factor when for example magnetization curves are being plotted on current transformers. In this case, the amplitude of the testing signal changes as a function of the mains voltage and the load. With standard commercial testers employing manually operated variable transformers it is also not possible to perform automatic test sequences giving repeatable measurements. Repetitive testing operations, such as the plotting of magnetization curves on transformers of identical design for example, therefore have to be carried out by qualified personnel, and this takes time.
To generate usable testing currents and testing voltages, the conventional practice is often to use power amplifiers but these are large, heavy, and expensive. Conventional power amplifiers of this kind are not suitable for light, transportable testing devices and what in fact need to be found in this case are solutions that are optimized in respect of weight and the space they take up.
Another problem that is found with conventional testing devices is that the measurements acquired by the testing device during a measuring operation can generally only be recorded by hand. Particularly when electrical systems are being commissioned, it is necessary for the tests to be properly documented. Occasionally the testers are also provided with a small printer or a PC interface. However, no complete solution for the automatic generation of a test record is known for primary tests.
It is clear from what is said above that there is a great need for a transportable testing device that is capable of being used flexibly and is not confined to specific applications, but in principle, can be used for testing various different power-engineering test-pieces operated at high currents and/or high voltages as desired.
The portable testing device according to the invention comprises a controllable converter device, in the form of a (switched-mode) power amplifier or power converter for example, which is to be connected to a source of supply voltage such as to the mains voltage for example. The portable testing device according to the invention further comprises a matching transformer having a plurality of switchable secondary windings to which a rest-piece on which measurements are to be made is removably connected. Also provided are control means which on the one hand control the controllable converter device in such a way that a desired testing signal is applied to the test-piece via the matching transformer or is fed to the test-piece, and which on the other hand acquire and preferably also evaluate analog or digital measurement signals which in each case define a measured parameter of the test-piece which adjusts itself in response to the testing signal generated. For this purpose, the control means may comprise a controller and/or a computer and/or a digital signal processor.
The above-mentioned control means may be so designed that they perform the appropriate test sequences automatically as a function of specific preset test procedures and for this purpose automatically control the controllable converter device and/or the matching transformer. The measurements obtained as a result of a test can be stored in the testing device itself, so that a test record is automatically produced for each tests which, via a suitable interface, can also be downloaded by an external computer. In addition to this, each test record can preferably serve at the same time as a master or template for a further test in which similar test-pieces are to be tested. Such test procedures can be stored in the device concerned beforehand or can be created by means of suitable input means such as a keyboard combined with a display unit. It is also conceivable for the desired test procedures to be downloaded from an external computer into the portable tester via a suitable interface.
The use of a digital signal processor makes it possible for a testing signal which in principle can be as desired to be applied to the test-piece which is connected at the time by controlling the controllable converter device in a suitable way. The use of a digital signal processor also ensures that the acquisition of the measurement signal can take place synchronously with the generation of the testing signal, so that it is possible for tests to be conducted in real time.
The control means of the portable testing device according to the invention are preferably so designed that they close a regulating circuit for regulating the testing signal emitted via the matching transformer. By monitoring the voltage or current in the secondary windings of the matching transformer, the voltage or current value of the testing signal emitted is regulated to a preset value and made independent of fluctuations in mains voltage. What is also possible is regulation where a sinusoidal testing signal is generated even when the impedance of the test-piece connected to the matching transformer is not linear.
It is particularly advantageous if the testing signal generated by the portable testing device is generated in synchronization with a given reference signal, such as the mains voltage for example. When this is the case it is even conceivable to have a large-scale testing system having a number of testing devices according to the invention which can be jointly synchronized via the same reference signal, via for example the mains voltage, a given control voltage or a GPS (global positioning system) signal.
In the context of the present invention, there is thus proposed a fully automatic portable testing device that can supply both high currents and high voltages. For this purpose, one or more internal sources which are formed by the previously described converter device are connected to at least one matching transformer which is capable of being changed over and which on the one hand provides electrical isolation on the output side and on the other is responsible for matching the amplifier output of the internal source concerned to the high-current or high-voltage circuit connected to the matching transformer. If the controllable converter device comprises a switched-mode power amplifier as the internal current or voltage source, the power amplifier preferably supplies an output voltage of 250 V and an output current of 20 A for example which is matched to the relevant high-current circuit (e.g. 5 V, 1000 A) or high-voltage circuit (e.g. 2000 V, 2.5 A) by means of the matching transformer. The particular reason for which this scheme is possible is because either high testing currents or high testing voltages are needed for testing current converters or transformers, voltage converters or transformers, industrial amplifiers, etc. in commissioning tests on power stations, transformer substations or the like, but not high testing currents and high testing voltages at the same time. The testing currents or voltages supplied by the portable testing device can have their amplitude and phase shift for example freely programmed by the control means described above, which can also comprise an externally connectable control.
By means of the portable testing device according to the invention, both a high-current source for direct and alternating current and a high-voltage source and a preferably multi-channel measuring means are incorporated in a compact and easily transportable device, in which case the measuring means can be designed to measure voltages, currents, phase angles, powers, resistances, tripping times and the like. Rather than a variable transformer, a switched-mode power amplifier is preferably used to generate the desired testing signal, in which case the testing can be controlled by the above-mentioned control means and testing sequences which would otherwise have to be performed manually at some expense in terms of time can take place fully automatically (such as the plotting of magnetization curves of current transformers). What is more, such a power amplifier, if appropriately controlled, makes it possible even for non-sinusoidal testing signals and harmonics to be generated, which is advantageous for estimating response characteristics at fairly higher frequencies for example. It is also possible for non-symmetrical testing signals to be generated to test the polarity of the wiring of the test-piece. At the same time the portable testing device proposed in the context of the present invention can also make use of the synergy of the current and voltage sources fitted for other testing duties, such as xcexcxcexa9 measurement for example. It is true that this calls for a certain added complication to the hardware and software of the testing device, but this will change the weight and size of the testing device or tester to only an immaterial degree.
As has already mentioned, the control means of the testing device according to the invention are used to acquire both analog measurement signals and digital measurement signals. The digital measurement input of the control means according to the invention in particular is of special importance because the test-pieces to be tested with the testing device according to the invention are becoming increasingly complex and in future unconventional current converters for example will be provided with direct digital interfaces and will thus no longer supply, as they have done so far, an analog secondary current (of the order of between 1 A and 5 A for example) but will be connected via a bus straight to the relevant station services management system. The testing of such unconventional current converters (for polarity, for transformation ratio or for transient response for example) is not possible with the testers known at the moment.